The present invention relates to improvements in servo-steering control means for vehicles, of the type which comprise a jack intended to actuate the steering mechanism, a source of fluid under pressure for supplying the jack, a slide valve for distributing fluid under pressure to the jack, this slide valve being controlled by means sensitive to the angular separation between a drive shaft and a shaft connected to the steering mechanism, these two shafts being mechanically connected in rotation with a certain play.
In U.S. Pat. No. 3,791,475 filed Mar. 28, 1972 and granted Feb. 12, 1974, servo-steering control means are provided which consist principally of means for controlling the distributor slide valve comprising, on the one hand, two members rotatable about a common geometric axis, respectively connected in rotation, by drive means having the same ratio, one with the drive shaft, the other with the shaft coupled to the steering mechanism and, on the other hand, means connected to the distributing slide valve adapted to transform the angular separation of the rotary members into longitudinal movement of the slide valve.
It is generally recognised that to ensure operation with low friction of a servo-steering control means according to the aforementioned patent, and due to the fact of the manufacturing tolerances, the mechanical couplings between the various constituent elements of the servo-steering control mechanism are inevitably effected with a certain play. This play has the drawback of causing a slight lag in the driving of the distributing slide valve when the direction of the angular movement of the drive shaft reverses with respect to that of the shaft connected to the steering mechanism.
A first object of the invention is to improve further the sensitivity, precision, and fidelity of power steering apparatus of this type.
A second object of the invention is to provide servo-steering control means of the above-defined type which overcome the above-mentioned drawback.
Another object of the invention is to provide servo-steering control means ensuring constant take-up of any play occurring in the kinematic linkages comprised between the distributing slide valve and respectively the drive shaft and the shaft connected to the steering mechanism.